Heated Greenhouse

I have a 26 foot high tunnel with a tent stove.  Frankly, I have found that composting raised beds do good job of heating it.  The stove is for brief, extreme, temperature plunges.  I also keep over 100 gallons of water in it.

What do you think about solar panels to make heat greenhouse? I think it is safe, cheap and good for environment.

I'm thinking solar electric panels would be too inefficient to heat a greenhouse.  Solar thermal may be worthwhile but you'd need a lot of them.  Better greenhouse design (insulation, passive solar) is probably where I'd start my efforts.